There are different causes of GERD which can require different treatments/diets. If you can afford it I strongly suggest you get you get your dog scoped to find the actual cause. It could be megaesphogus like you assume or a hiatal hernia or a couple other things.
In the mean time some things seem to work across the board. The low fat foods and 4-6 small meals. Avoid all grains, starchy vegs, legumes, refined sugar. Give pumpkin or squash instead. Raw, unpasteurized honey. No/low fat cottage cheese or kefir. Naturopath options like enzymes & probios.
Some think it’s a good idea to feed from a raised bowl. I had a dog with very mild reflux who was fed from a raised bowl. He eventually died of bloat. Which I later found out that there can be (not always) a connection between reflux & bloat. No one has yet to figure out weather a raised bowl is good or bad for dogs, it is suggested to raise the bowl only a couple inches from the floor. Dogs are designed to eat standing up from the ground, but some need a very slightly elevated dish. (I tend to agree feeding dogs & horses with ground feeders. It is more natural.)
I have a dog right now who has some GI issues as a result of a lot of antibiotic treatments. The longer she goes without a meal, the more likely she is to have a rumbling belly, nausea, discomfort, etc. Smaller meals throughout the day helped her a lot when she was really sick.
